Tandem Genetic Duplications in Bacteriophage Lambda: Our objective is to learn the mechanism by which mutants bearing tandem genetic duplications arise in phage lambda. Non-selective methods are being worked out for isolating and determining the frequency of phage mutants carrying tandem duplications. The endpoints of a duplication are mapped by electron microscopy of DNA heteroduplexes. Experiments are in progress to determine if duplications arise by an intermolecular event, recombining segments of two genomes, or by an intramolecular event. Mechanism of Protein Folding: We are studying the low pH, reversible unfolding transitions of simple, small proteins such as ribonuclease A and chymotrypsinogen A to learn how to detect and characterize intermediates, and to use these to work out the pathway and mechanism of folding. Fast, kinetic studies of these transitions show that they are complex with both fast and slow reactions, and consequently that they are not simple, 2-state, folded reversible yields unfolded reactions. Current work shows that both the fast and slow refolding reactions of ribonuclease A yield native enzyme as product, and suggests that complete refolding can take place in the time range of 10-100 milliseconds when the disulfide bonds are intact.